1. Field of the Invention
The invention relates to an adjustment method for a vehicle automatic transmission that includes a hydraulic control circuit including linear solenoid valves that control the pressures supplied to hydraulically-driven friction engagement elements, and a valve control unit that outputs the drive currents to drive the linear solenoid valves. More specifically, the invention relates to an adjustment method for calculating correction values that are applied to the control command values used to adjust the drive currents so that the correlations between the drive currents supplied to the linear solenoid valves and the effective pressures exhibit nominal characteristics.
2. Description of the Related Art
There is an automatic transmission test system that includes a component tester that detects the characteristic values of components which form a vehicle automatic transmission before assembly of the vehicle automatic transmission is completed; a storage medium that stores the characteristic values detected by the component tester, and a finished-product test device that tests the fully-assembled automatic transmission using the characteristic values stored in the storage medium.
With the automatic transmission test system, the characteristic values of the components that form the automatic transmission, the characteristic values of component assemblies each of which is an assembly of the components, and the characteristic values of assemblies of the component assemblies are measured by the component tester and a component assembly tester. Corrections are then made to the characteristic values if needed, and the characteristic values or the correction values are stored in the storage medium. During the finished-product testing step, the fully-assembled automatic transmission is tested based on the characteristic values of the automatic transmission stored in the storage medium.
A conventional vehicle automatic transmission test system is described in, for example, Japanese Patent Application Publication No. 2004-212182 (JP-S-2004-212182). In the described vehicle automatic transmission test system, the output pressure SLS (Kpa) output from the same linear solenoid valve are measured a predetermined number of times, and the average value thereof is used as the measured value. Then, the deviation of the measured value from the median of the output pressures SLS output from the linear solenoid valve according to the PPC standard is calculated, and the deviation is used as the hydraulic pressure correction data. However, in such conventional vehicle automatic transmission test system, changes in the characteristic values such as pressure loss that may occur while the output pressure output from the linear solenoid valve passes through a hydraulic control circuit, a connection sealing, etc. and finally becomes the engagement pressure used to engage a friction engagement element, namely, the supply pressure, are not taken into account. For example, if the pressure difference between the output pressure and the pressure detected at a hydraulic pressure detection portion is used as the pressure difference between the output pressure and the supply pressure supplied to the hydraulically-driven friction engagement element, correction errors may occur. Even if corrections are appropriately made to compensate for the variations in the valve characteristics of the linear solenoid valves, the variations in the characteristics of the hydraulically-driven friction engagement elements, particularly, the variations in the pressures at which engagement of the hydraulically-driven friction engagement elements is started (piston-end pressures) are not taken into account. Therefore, the torques that are transferred by the hydraulically-driven friction engagement elements are not accurately controlled, which may cause inconveniences, for example, torque shock may be caused when the hydraulically-driven friction engagement element is engaged, namely, shift shock may be caused in the automatic transmission.
In the hydraulically-driven friction engagement elements, even if the same hydraulic fluid pressure is supplied to the hydraulically-driven friction engagement elements, the hydraulically-driven friction engagement elements are not engaged in the same manner and the pressures at which engagement of the hydraulically-driven friction engagement elements is started vary due to the variations in the moving resistance of the pistons and the variations in the return springs. Accordingly, even if the hydraulic control is executed with the variations in the valve characteristics of the linear solenoid valves taken into account, torque shock may be caused when the hydraulically-driven friction engagement elements are engaged, namely, the shift shock may be caused in the automatic transmission. In the hydraulic control for the vehicle automatic transmission, it is also important to take the variations in the engagement/disengagement characteristics of the hydraulically-driven friction engagement elements into account.